C++ ─── string的完整模拟实现

本博客实现了string的常见接口实现

下面是用到的一些函数，供大家回顾复习

改进1：流提取的改进

        原来的代码中流提取中是一个一个字符提取，扩容频率太快，消耗太多

采用buff的方式，buff在栈上，开空间快。

istream& operator>> (istream& is, string& str){str.clear();char buff[128];int i = 0;char ch = is.get();while (ch != ' ' && ch != '\n'){buff[i++] = ch;//0 - 126if (i == 127){buff[i] = '
';str += buff;i = 0;}ch = is.get();}if (i != 0){buff[i] = '
改进二：拷贝构造和赋值重载的改进
';str += buff;}return is;}

//bit::string s1(s2)  原来的写法string::string(const string& s){_str = new char[s._capacity+1];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;}//改进后//bit::string s2=s1;string::string(const string& s){string tmp(s._str);std::swap(tmp._str,_str);std::swap(tmp._size,_size);std::swap(tmp._capacity, _capacity);}string::string(const string& s){string tmp(s._str);swap(tmp);}注意有些平台s2没有初始化（this指针是随机制），s2与tmp交换后，tmp的_str为随机值，出了函数，tmp会调用析构函数就会崩解决方案：在.h文件定义中都加上缺省值例如：private://char _buff[16];char* _str=nullptr;size_t _size = 0;size_t _capacity = 0;

​//原来的    string& string::operator=(const string& s){if (this != &s){char* tmp = new char[s._capacity + 1];strcpy(tmp, s._str);delete[] _str;_str = tmp;_size = s._size;_capacity = s._capacity;}return *this;}//改进后//s1 = s3string& string::operator=(const string& s){if (this != &s){string tmp(s._str);swap(tmp);}return *this;}string& string::operator=(string tmp){    swap(tmp);    return *this;}​

        传统写法就是1.开空间2.拷贝数据

        使用现代写法（利用构造函数）改进, 利用构造函数，两者实际效率一样但是现代写法更简单快捷

string.h

#define _CRT_SECURE_NO_WARNINGS 1#pragma once#include#includeusing namespace std;namespace bit{class string{public:typedef char* iterator;typedef const char* const_iterator;iterator begin();iterator end();const_iterator begin() const;const_iterator end() const;//string();string(const char* str = "");string(const string& s);string& operator=(const string& s);~string();const char* c_str() const;size_t size() const;size_t capacity() const;char& operator[](size_t pos);const char& operator[](size_t pos) const;void reserve(size_t n);void push_back(char ch);void append(const char* str);string& operator+=(char ch);string& operator+=(const char* str);void insert(size_t pos, char ch);//在pos前面插入void insert(size_t pos, const char* str);void erase(size_t pos = 0, size_t len = npos);//从pos开始删除size_t find(char ch, size_t pos = 0);size_t find(const char* str, size_t pos = 0);void swap(string& s);string substr(size_t pos = 0, size_t len = npos);bool operator(const string& s) const;bool operator=(const string& s) const;bool operator==(const string& s) const;bool operator!=(const string& s) const;void clear();private://char _buff[16];char* _str;size_t _size;size_t _capacity;//  //const static size_t npos = -1;// ֧//const static double N = 2.2;const static size_t npos;};istream& operator>> (istream& is, string& str);ostream& operator _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);//复制字符串最后是''delete[] _str;_str = tmp;_capacity = n;}}void string::push_back(char ch)//等价与+=(char ch){if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}_str[_size++] = ch;_str[_size] = '';}void string::append(const char* str)//等价与+=(const char* ch){size_t len = strlen(str);if (_size == _capacity){size_t newcapacity = _capacity + len;reserve(newcapacity);}//直接从str末尾加入字符串strcpy(_str + _size, str);_size += len;}string& string::operator+=(char ch){push_back(ch);return (*this);}string& string::operator+=(const char* str){append(str);return (*this);}void string::insert(size_t pos, char ch){assert(pos  pos){_str[end] = _str[end - 1];--end;}_str[end] = ch;_size++;}void string::insert(size_t pos, const char* str){size_t len = strlen(str);assert(pos  pos){_str[end] = _str[end - len];--end;}_size += len;//while (len)//{//_str[end + len - 1] = str[len-1];//--len;//}memcpy(_str + pos, str, len);}void string::erase(size_t pos, size_t len){assert(pos  _size - pos){_str[pos] = '';_size = pos;}else{strcpy(_str + pos, _str + pos + len);_size -= len;}}size_t string::find(char ch, size_t pos){for (size_t i = pos; i  _size - pos){string sub(_str + pos);return sub;}else{string sub;sub.reserve(len);for (size_t i = 0; i  (istream& is, string& str){str.clear();char ch = is.get();while (ch != ' ' && ch != '\n'){str += ch;ch = is.get();}return is;}ostream& operator